Field verification for the effectiveness of continuity diaphragms for skewed continuous P/C P/S concrete girder bridges.

664559685Final report; April 2006-March 2008.PDFTech ReportFHWA/LA.09/440LTRC Project No. 06-3STState Project No. 736-99-1373Diaphragms (Engineering)Prestressed concrete bridgesContinuous girder bridgesTestingLouisianaLouisiana Transportation Research CenterSaber, AzizMothukuri, Ajay K.Arasangi, PrashantLouisiana Transportation Research CenterLouisiana. Dept. of Transportation and DevelopmentNTL-HIGHWAY/ROAD TRANSPORTATION-Bridges and StructuresNTL-HIGHWAY/ROAD TRANSPORTATION-MaterialsUS Transportation CollectionThe research presented herein describes the field verification for the effectiveness of continuity diaphragms forskewed continuous precast, prestressed, concrete girder bridges. The objectives of this research are (1) to performfield load testing on the Burlington Northern Santa Fe (BNSF) overpass and compare measured strains with thosedetermined through the theoretical analyses and (2) to study the effects of continuity diaphragms on stresses anddeflections from truck loading on bridge deck slab and bridge girders.The current design concept of continuity diaphragms was examined to determine the effectiveness of thediaphragms in skewed bridges. The bridge parameters that were considered include skew angle, length of thespan, beam spacing, the ratio of beam spacing to span (aspect ratio), and the ratio of girder stiffness to that of theslab. A prestressed concrete bridge with continuity diaphragms and a skewed angle of 48\uc2\ub0 was selected by a teamof engineers from the Louisiana Department of Transportation and Development (LADOTD), the LouisianaTransportation Research Center (LTRC), the Federal Highway Agency (FHWA).The BNSF Overpass Bridge is located on US-90 in Jennings, Louisiana. The field verification was performedusing a comprehensive instrumentation plan and live load tests as described in this report. The field andtheoretical results from this study provided a fundamental understanding of the load transfer mechanism throughthese diaphragms of skewed, continuous span bridges. The findings in this study on stresses, strains, anddeflections in the bridge deck and girders indicated that the effects of the continuity diaphragms on skewedcontinuous span precast prestressed concrete girder bridges were negligible. The results presented in this reportalso confirmed the theoretical findings published in LTRC Report 383 titled \ue2\u20ac\u153Continuity Diaphragm for SkewedContinuous Span Precast Prestressed Concrete Girder Bridges.\ue2\u20ac? Continuity diaphragms used in prestressedconcrete girder bridges on skewed bents provided additional redundancy in the bridge but caused difficulties indetailing and construction. As the skew angle increases or the girder spacing decreases, the construction becomesmore difficult and the effectiveness of the diaphragms becomes questionable. It is also recommended that the useof continuity diaphragms be evaluated based on the need for the enhanced structural redundancy, the reducedexpansion joint installation and maintenance costs, and the associated construction difficulties and costs. Theoutcome of this research will reduce the construction and maintenance costs of bridges throughout Louisiana andthe United States